<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>栅格系统布局</title>
    <style>
        li {
            list-style: none;
        }

        .row {
            width: 100%;
        }

        .row:after {
            clear: left;
            content: '';
            display: table;
        }

        [class^='col'] {
            float: left;
            background: #ff0000;
        }

        .col_1 {
            width: 25%;
        }

        .col_2 {
            width: 50%;
        }

        @media (max-width: 768px) {
            .row {
                width: 100%;
            }

            [class^='col'] {
                float: none;
                width: 100%;
            }
        }
    </style>
</head>
<body>
<div class="row">
    <header>页头</header>
</div>
<div class="row">
    <li class="col_1">东皇</li>
    <li class="col_2">紫薇</li>
    <li class="col_3">玉皇</li>
</div>
<div class="row">
    <footer>页尾</footer>
</div>
</body>
</html>